1. Field of the Invention
The invention relates to a record carrier comprising a disc-shaped substrate with a radiation-sensitive information layer. The record carrier is provided with information areas arranged in a spiral or concentric track pattern and is intended for recording and/or reproduction, via a radiation beam, of digitally coded information having a fixed bit frequency in the information areas.
The invention further relates to an apparatus for manufacturing such a record carrier in which the track pattern is inscribed by a radiation beam before the information layer is applied.
The invention also relates to an apparatus for recording information on such a record carrier comprising a light source and an optical system for directing a light beam to the information areas of said record carrier, a recording circuit for modulating the light beam depending on the digital signal to be recorded, and an optical system comprising a detector for detection of radiation which is reflected or transmitted by the record carrier.
The invention also relates to an apparatus for reading such a record carrier, in whose information areas digital information has been recorded, by means of a light beam which scans the information areas. The apparatus comprises an optical system and a detector for detecting the radiation reflected or transmitted by the recording areas and a read circuit for extracting the digital information signal from the detected radiation.
2. Description of the Related Art
A record carrier of the type mentioned in the preamble as well as apparatus for recording and/or reading information on and/or from such a record carrier, is disclosed Netherlands Patent Application No. 7802859 which has been laid open to public inspection and corresponds to U.S. patent application Ser. No. 140,409, filed Apr. 14, 1980. In the record carrier described in that application, the information areas alternate with synchronization areas each containing the address of the information area that follows such a synchronization area. When such a record carrier is used the clock generation is intricate and sometimes not very reliable. During reading it is possible, though intricate, to derive a clock signal from the recorded data signal and from the information signals contained in the synchronization areas. When the data signal is written in the information areas, the clock generation is even more intricate, because then only the information contained in the synchronization areas is available. In that case a clock generator may be used which, during reading of the synchronization areas, can be synchronized with the information contained in the synchronization areas by means of a phase-locked loop. Apart from its complexity, such an arrangement has the additional drawback in that at the beginning of each synchronization area the phase-locked loop must be locked in again. The synchronism of the record carrier motion of the process of recording data in the information areas is not reliable, so that not every information area is utilized up to the end because space is to be reserved in order to allow for the effect of possible speed variations of the record carrier and of the information recording process as a result of the drift of the clock generator frequency. In the Patent Application it has, therefore, been proposed to include additional synchronization areas in the information areas, which mitigates the above problems but does not eliminate them and which reduces the information storage capacity of the record carrier. In record carriers in which no synchronization areas are employed between the information areas, such as for example record carriers for recording digitally coded audio signals, the clock generation is even more intricate.